Directed information flow: a model free measure to analyze causal interactions in event related EEG-MEG-experiments - PubMed (original) (raw)

Hermann Hinrichs et al. Hum Brain Mapp. 2008 Feb.

Abstract

In a study that combined event related potential (ERP) and magnetic field (ERMF) data, we analyzed the timing and direction of information flow between striate (S) and extrastriate (ES) cortex by applying a generalized mutual information measure (DIT for "directed information transfer") during a visual spatial attention task. ERP and ERMF recordings showed that selective attention to stimulus arrays in one visual field enhanced late responses (around 200 ms after the stimulus presentation) that were localized in S (ERMF) and ES (ERP) cortex. The results of the DIT analysis indicate there is a significant attention related increase in the flow of information back from ES to S cortex at around 220 ms, with an associated decrease in the flow of information forward from S cortex to ES cortex. These results support the hypothesis that a feedback mechanism guides attention-related processing in primary visual cortex and provide evidence that DIT can by used to evaluate the direction of information flow between cortical areas.

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Figures

Figure 1

Figure 1

Left: Cross correlation between the simulated data sets (x and y, see methods section) at selected time points (see index) for a lag (delay) of ±10 sampling intervals. Right: Comprehensive overview for the whole period.

Figure 2

Figure 2

Information flow estimated for the simulated data sets (x and y). Upper row: Flow from y to x. Left: Temporal distribution of the flow at individual time points up to a delay (lag) of 10 sample intervals. Right: Comprehensive overview for the whole period Lower row: Same but for opposite flow direction, i.e., x to y.

Figure 3

Figure 3

ERP‐ and ERMF‐scalp topography (grand average, spline interpolation) of the late attention effect. The signals analyzed in the present study were acquired from the sensors marked by black dots.

Figure 4

Figure 4

A: The enhanced cumulated information flow from contralateral extrastriate (ES) to striate (S) cortical areas, related to the flow (S→ES) under the “attend” and the “neutral” condition. Both the EEG and MEG data were included when deriving the flow values (see methods section for details). All data were low pass filtered at 24 Hz cut off frequency. B: Single subject data of the contralateral flow form extrastriate to striate versus the flow from striate to extrastriate cortex. Same normalization as in subfigure A. C: Global field power for the event related potentials (ERP) and the event related magnetic fields (ERMF). The data reflect the attend left + right collapsed condition.

Figure 5

Figure 5

Excess of cumulated information flow towards striate areas (see Fig. 4 for the normalization) at various delays of interaction between contralateral extrastriate (ES) and striate (S) areas under the “attend” condition. The curve was derived at a latency of 220 ms where the cumulated difference flow between ES and S is largest under the “attend” condition. Levels of significance: “*” = P < 0.05, “**” = P < 0.01, “***” = P < 0.005, “****” = P < 0.001.

Figure 6

Figure 6

Difference between cumulated flow of information (both ES→S and S→ES observed under the “attend” and the “neutral” condition. All values are related to the flow obtained at the neutral condition. The data were low pass filtered at 24 Hz cut off frequency.

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